Buying a plane and getting it to where you want to go help

Me and a couple friends of mine are thinking about buying and splitting a 1979 Cessna 172N. The price is right and the hours are relatively low and we were wondering how much it would cost to make it perfect. What would be the cheapest GPS available for us and what would be better, panel install or hand held/mount. We are able to cover fuel and MX with a friend that would use it in its spare time in return, but would really like some sort of GPS. 
